Development of the spinal cord EMBRYOLOGY Flashcards Preview

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Flashcards in Development of the spinal cord EMBRYOLOGY Deck (95):
1

the notochord secretes what?

noggin and chordin

2

what do noggin and chordin do

induce the overlying ectoderm to differentiate in a very specific manner

3

what does the notochord signals the development of?

spinal cord (ectoderm)

vertebral column (mesoderm)

4

Day 19

Neurulation starts

neural ectoderm forms --> called the neural plate

is signalled by the notochord

5

what does the neural plate give rise to?

central nervous system
neural crest cells

6

Day 20

lateral edges start to fold towards one another forming neural groove

7

Day 22, 23

lateral edges fuse

forming neural tube

fusion begins in the cervical/neck region of the embryo and progresses cranially and caudally

8

what day does the caudal neuropore close?

Day 27

9

what day does the cranial neuropore close

Day 25

10

what does the neural tube give rise to ?

spinal cord and brain

11

if there was a defect during formation of the neural tube epithelium, which of the following cell types would be unaffected?

dorsal root ganglion b/c they are part of the peripheral nervous system

12

Neural crest cells

gives rise to all cells of the PERIPHERAL NS

Sensory ganglia of cranial and spinal nerves
Autonomics
-(all peripheral parasympathetic and sympathetic ganglia)
-sympathetic chain ganglia
-prevertebral sympathetic ganglia
-parasympathetic ganglia

Schwann cells

Meninges

13

classic signs of neural crest cell deformities

peripheral nervous system defects

craniofacial defects

heart defects

14

what are the 3 different regions that form in the neural tube as a result of neuron migration from the neuroepithelium?

Ventricular

mantle

marginal zones

15

Ventricular zone

middle inner layer

embryo--> thick, pseudostratified neuroepithelium

adult --> very reduced b/c neurogenesis has stopped--> composed of a simple layer of EPENDYMAL cells

16

Mantle layer


where the cell bodies take up residence

mantle in adults forms the gray matter

motor neurons migrate ventrally (form basal plate)
sensory neurons migrate dorsally (forma alar plate)

17

basal plate in adults

motor neurons have migrated ventrally to form this area

forms ventral motor horn in adult
cell bodies of origin for motor nuclei are located here

18

Alar plate

sensory neurons have migrated dorsally to form this region

becomes the dorsal sensory horn (where sensory information enters the spinal cord)

19

marginal layer

outermost layer, composed of nerve processes

where axons and dendrites are located, which can be myelinated

WHITE MATTER IN adults

20

spinal nerve

motor and sensory components

21

motor part of nerve

cell bodies located in the basal plate of the mantle layer

form ventral motor root of the spinal nerve

eventually merging with the sensory component

22

sensory part of nerve

cell bodies located in the dorsal root ganglia


23

what is the dorsal root ganglion formed from

neural crest cell

24

dorsal root ganglion

send peripheral process outward which forms the dorsal sensory root of the spinal nerve

send central process into the alar plate

25

mixed spinal nerve

ventral nerve root and dorsal nerve root
31 pairs

cervical first
then thoracic
lumbar
sacral
coccygeal

26

spinal cord differential growth

8 weeks - spinal cord extends the entire length of the vertebral column (so when spinal cord segments and spinal nerves form they line up with vertebrae across from it)

in newborn the spinal cord ends at LV4-LV5

in the adult the spinal cord ends at about LV1-LV2

27

where does the spinal cord end in the adult

at LV1-LV2

28

what is the somite doing?

guiding formation of spinal nerves

sends out signals!!

29

each spinal nerve has...

its own somite

30

somites give rise to

dermatomes

31

dermatomes

strip of skin innervated by one spinal nerve

32

somite splits into myotome too!

a group of muscles innervated by one spinal nerve

33

when do the ventral and dorsal rami form?

when the somite splits into dorsal and ventral portions

34

epimere

innervatd dorsal ramus

forms back structures

35

hypomere

innervated by ventral ramus

forms rest of trunk and limbs

36

spina bifida occulta

results when vertebral arches os spinal cord fail to fuse.
typically does not involve meninges or nervous tissue

often marked by a small patch of hair over the lumbosacral spinal cord region

37

spina bifida with meningocele

involves the meninges

38

spina bifida with meningomyelocele

involves meninges and spinal cord

39

spina bifida with myeloschisis

the most severe form of spina bifida

neural plate fails to elevate and fold

very underdeveloped

40

sclerotome of the somite forms the ...

axial skeleton (vertebral column, sternum, ribs, portion of the skull)

organizes loosely around neural tubea

41

dermotome of the somite

just deep to the ectoderm

dermis

42

myotome of the somite

skeletal muscle

43

what about somites??

arises from paraxial mesoderm

44

vertebral column resegmentation

sclerotome divides into cranial and caudal portions

caudal half fuses with cranial half of sclerotome below it
this fusion forms the vertebrae

after resegmentation myotome actually now spans two vertebral levels

45

what is the nucleus pulposus formed from

notochord

46

annulus fibrosis

formed from mesenchymal cells which remain between the cranial and caudal portions of the original sclerotome

47

hemivertebrae

most often causes congenital scoliosis

half a vertebrae b/c only one vertebrae ossified

48

Klippel-Feil syndrome

results in fusion of vertebrae (most often cervical)

fusion happens when resegmentation doesn't take place (doesn't split)

results in a short neck and restricted neck movements

49

what do ribs develop from?

develop from costal processes of the 12 thoracic vertebrae

50

sternum

NOT FROM SOMITE

but rather from LATERAL plate mesoderm

forms from the fusion of two sternal bars

51

pectus excavatum

depression in chest (anterior thoracic wall sunken-in)

caused by ribs growing in excess

52

pectus carinatum

anterior thoracic wall protrudes

"pigeon" chest

ribs grow in excess

53

all skeletal muscle comes from the ...

myotome of the somite

54

myotome splits into...

dorsal and ventral portions


dorsal-->

55

epimere

dorsal part after myotome split

innervated by dorsal primary rami

gives rise to intrinsic back muscles
(erector spinae, splenius, transversospinal group, intersegmental group)

56

hypomere

ventral part after myotome splits

innervated by ventral rami

gives rise to anterior and lateral neck musculature, trunk muscles and limbs

57

why do our muscles have multiple myotomes and more than one level of innervation

b/c a myotomes can split!

58

splitting of myotomes longitudinally

trapezius and sternocleidomastoid muscles

59

skeletal muscle myogenesis

1) mesoderm cells differentiate into myoblasts (primordial muscle cells)

2) myoblasts ellongate and fuse together to form myotubes

3) contractile filaments appear in the cytoplasm of the myotube, now called a muscle fiber with sarcomeres

60

why are skeletal muscle multinucleate?

b/c multiple myoblasts fuse

61

Poland syndrome

Absent or underdeveloped pectoralis muscles

usually unilateral, right side affected

most cases include syndactyly of the fingers

cause is unknown but believed to involve loss of blood supply to chest wall during development

62

somatic layer of LATERAL PLATE mesoderm will give rise to what?

connective tissues of limbs

-bones
tendons
ligaments
dermis
blood
blood vessels

63

axial skeletal comes from

paraxial mesoderm

64

surface ectoderm gives rise to

epidermis

65

myotome of somites gives rise to

all skeletal muscle of limbs

66

upper limb limb buds show up when?

Day 25-26

67

lower limb limb buds show up when?

day 27-28

later than upper limb
CRANIAL TO CAUDAL SEQUENCING

68

what is the AER and where is it?

apical ectodermal ridge

signals limb growth

located at the apex of the limb bud

69

hand and foot plates

form at week 5

distal ends of limb buds flatten to become paddle like

separated from limb bud by circular constriction

70

what are digital rays

4 zones of APOPTOSIS along AER separate hand and footplates into 5 digital rays (five separate areas of AER)

6th week--> upper limb
7th week --> lower limb

71

ectrodactyly

one missing digit or multiple missing digit

72

brachydactyly

shortened digits

AER fail to lay down enough mesoderm

73

polydactyly

too many digits

one extra apoptotic zone

74

syndactyly

fusion of digits

not enough apoptotic cell death

osseous or dermal fusion of phalanges

75

amelia

lack of limb formation
no AER formed or it doesn't signal properly

76

meromelia

partial limb formation (phocomelia)

77

what is the main signal for proximal and distal growth in limbs?

AER

shoulder (proximal) to wrist (distal)

78

what is the main signal for dorsal and ventral

dorsal (elbow and knee)

ventral (palm of hand, plantar surface of foot)

79

anterior posterior axis of limb

defines thumb and great toe as anterior

little toe and little finger posterior

ZPA responsible for signalling this

80

ZPA

zone of polarizing activity

releases retinoic acid which forms gradient that establishes anterior and posterior axis

81

limb ossification

starts with endochondral ossification of lateral plate mesoderm

lay down mesenchymal model

then form cartilaginous model (week 5)

blood vessels migrate into and form primary site of ossification (7th week)

mesodermal cells differentiate into osteoblasts which then secrete bone matrix

NOTE some bones begin ossification after birth

82

joint formation

site of contriction leads to signalling cascade that leads to cell death

clears out mesenchymal cells and forms the interzone

interzone forms joint cavity

mesodermal cells then form cartilage/capsule etc.

83

when do secondary ossification centers form?

mostly after birth

important for growth

84

muscle formation in the limb

5th week -- myogenic cells from the myotome (hypomere portion) of the somite migrate into the limb bud (come in after cartilage)

myotomes pull in their ventral rami with them

muscles divide into anterior flexor and posterior extensor portions

85

myotomes that migrate into the upper limb

C5- T1

86

myotomes that migrate into the lower limb

L2-S3

87

limb rotation

upper and lower limb initially in exact same position (thumb and great toe directed lateral)

lower limb rotates 180 degrees medially so that the great toe becomes medial, knee directed anterior in adult

ends with the flexor compartments dorsal and the extensor compartments as ventral

88

Sensory limb innervation

sensory fibers are pulled into the limb as it elongates from the trunk

spinal nerves migrate along with dermatomes as they are pulled into developing limb

89

how is sensory innervation distributed in limbs?

Radially

spiral effect in lower limb-b/c of limb rotation

90

what is different about how dermatomes and myotomes form?

dermatomes are already established before limbs form

myotomes migrate in after limb has been established

91

limb motor innervation

migrate into limb longitudinally

motor innervation spreads down the limb

so upper limb C5 near shoulder T1 near fingers

L2 near hip and S3 near foot

92

phocomelia

absence of long bones

93

congenital clubfoot

abnormal position of foot: sole inverted, foot adducted and plantar flexed

common cause is oligohydramnios (too little amniotic fluid)

94

amniotic bands do what?

act as truncates

can circle and entrap portions of the fetus cutting off circulation as fetus develops and may cause amputations

95

congenital hip dislocation

underdevelopment of acetabulum and head of femur

laxity of joint capsule

dislocation occurs before birth

common with breech deliveries